JP2791568B2 - Fuel cell power generation system - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a power generation system for a fuel cell, and more particularly, to a fuel in which the amount of steam used for a reforming reaction of a fuel gas is reduced to improve the economic efficiency. The present invention relates to a battery power generation system.

[Prior Art] A fuel cell generates electricity by placing positive and negative electrodes across an electrolyte, supplying oxygen and hydrogen to each electrode, and artificially performing the reverse process of electrolysis. Depending on the type of electrolyte used, the electrolyte is roughly classified into an alkaline type, a phosphoric acid type, a molten carbonate type, a solid electrolyte type, and the like.

Among them, the molten carbonate type and the solid electrolyte type are operated at a high temperature, and there are almost no restrictions on the fuel gas composition, so that a fuel cell having higher power generation efficiency can be obtained.

These fuel cells use hydrogen and carbon monoxide gas as fuel gas.
Methanol, coal gas, etc. are used after steam reforming. The reforming includes an internal reforming type in which natural gas or the like is steam reformed inside the fuel cell and an external reforming type in which steam is reformed outside the fuel cell.

In a conventional solid electrolyte type internal reforming fuel cell,
In the structure shown in the figure, the following reforming reaction and electrode reaction occur at the cathode (hydrogen electrode).

Reforming reaction / shift reaction CH ₄ + H ₂ OCO + 3H ₂ CO + H ₂ OCO ₂ + H ₂ electrode reaction (solid electrolyte type, O ⁻ transmission type) Cathode O ⁻ → 1 / 2O ₂ + e H ₂ + 1 / 2O ₂ → H ₂ O CO + 1 / 2O ₂ → CO ₂ anode 1 / 2O ₂ → O ⁻ −e Thus, at the fuel electrode of the fuel cell, when producing (H ₂ + CO) gas by steam reforming of raw material hydrocarbons, Although a certain amount or more of steam is required, it is not preferable to supply the whole amount from the outside in terms of thermal efficiency.

[Problem to be Solved by the Invention] In order to improve such a problem, in an external reforming type phosphate type fuel cell as an effective use method of steam, it is generated along with the power generation reaction of the fuel cell. Waste heat is recovered as steam, and this is used as a raw material for the reforming reaction.

However, in such a conventional method, the saving of water vapor is not sufficient.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to reduce the amount of steam supplied from the outside and secure sufficient and necessary steam for reforming hydrocarbons. An object of the present invention is to provide a fuel cell power generation system with improved economy.

[Means and Actions for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventor has found that an internal reforming type fuel cell is divided into two or more stages and installed in the first stage. By supplying hydrocarbons and steam to reforming and power generation, by adding hydrocarbons to the gas containing steam flowing out of the first stage and supplying it to the second stage to reform and generate power, In addition, the present invention that solves the above-mentioned problem has been completed by recycling and reusing steam and carbon dioxide gas generated in the second stage and thereafter.

That is, the present invention relates to a power generation system using a fuel cell, in which the fuel cell is divided into two or more stages and installed, and hydrocarbons are added to a gas containing water vapor and carbon dioxide flowing out of the fuel chamber of the upstream fuel cell to add a hydrocarbon to the downstream. A fuel cell power generation system characterized in that it is used as a raw material for a fuel cell reforming reaction to generate power.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic diagram showing an internal reforming type fuel cell power generation system of the present invention.

In FIG. 1, 1 and 2 are fuel cells, 1a and 2a are fuel chambers, 1b and 2b are air quality, 3 is a fuel gas supply line, 4 is a steam supply line, 5 is a compressor, 6 is a cooler,
7 denotes a gas-liquid separator, 8a and 8b denote fuel units, 9a and 9b denote air supply lines, and 10a and 10b denote exhaust gas lines.

In the present invention, first, as shown in FIG. 1, two or more internal reforming fuel cells are provided. Steam required for reforming the fuel gas is supplied to the first stage. The method of supplying steam is
The steam generated in the boiler is supplied, and a part of the steam is used by recycling a part of the outlet gas of the fuel chamber of the second and subsequent fuel cells. Adding an excess of water vapor reforming reaction of the fuel quality of the fuel cell reduces the hydrogen partial pressure PH _2,
It is not preferable because the electromotive force drops. In order to reduce the amount of steam used by generating steam by boiler water supply, the steam generated by the electrode reaction is used.

The raw material gas (CH ₄ ) is supplied by being divided into one stage and two stages. Even if the raw material is liquefied petroleum gas or naphtha, a gas reformed into CH ₄ , H ₂ , CO, and CO ₂ can be obtained if a low-temperature steam reforming step is added, so that the present invention can be applied to the present invention. Split injection of CH ₄ to each fuel chamber, it is an object to use the steam generated in the fuel chamber, which can be made averaged partial pressure of hydrogen in the fuel cell, the electromotive force There is an effect that can be kept constant.

A part of the fuel cell outlet gas is cooled to condense and remove H ₂ O, then mixed with air and burned in contact, and then sent to the air chamber or mixed and burned without cooling. Into the air chamber to maintain the temperature of the room change reaction / power generation reaction.

As described above, in the present invention, power is generated by using the steam and the carbon dioxide gas flowing out of the fuel chamber of the upstream fuel cell as a raw material for the reaction of the downstream fuel cell. In addition, the steam and carbon dioxide gas flowing out of the fuel chamber are recycled and used as a raw material for a room change reaction of each fuel cell to generate power.

 The electrode reaction in the fuel cell is as follows.

Air electrode ^{_{(anode) 1 / 2O 2 → O -}} -e anode _{^{(cathode) O - → 1 / 2O 2}} + e The _{H 2 → 1 / 2O 2 +} H 2 O reforming _{reactions, (CH 4 + 2H 2 O} → CO ₂ + since 4H _2, a _{4H 2 + 2O 2 → 4H 2} O), eventually, the fuel _{electrode, CH 4 + 2O 2 → CO} 2 + 2H 2 O, the reaction of which occurred.

Thus, even if the steam generated at the fuel electrode is used for the re-rooming reaction, 2 moles of H ₂ O are generated per mole of CH ₄ ,
H ₂ O / CH ₄ = 2 can be maintained.

The present invention can be preferably applied to either the molten carbonate type or the solid electrolyte type as the fuel cell. In the molten carbonate type, a liquid carbonate such as potassium carbonate and lithium carbonate is used as an electrolyte at a temperature of 500 ° C. or higher. In a solid electrolyte fuel cell, zirconium stabilized with calcium oxide, thorium oxide, cerium oxide, yttrium oxide, or the like is preferably used.

In addition to the internal reforming type in which the fuel gas is steam reformed inside the fuel chamber as well as the external reforming type fuel cell provided that an external reformer is provided immediately before each fuel cell, the fuel cell is not limited to the internal reforming type. The invention can be suitably applied.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 100 g of methane gas was discharged from a solid electrolyte type fuel cell power generation device composed of multiple stages of an internal reforming type shown in FIG.
000Nl / hr, water vapor 200.000Nl / hr and S / C = 2.0
It was introduced into the supply line 1 of the stage.

A steam reforming reaction was performed at a temperature of each reformer of 900 ° C. and a pressure of 1.5 atm. The gas composition in the first-stage outlet line 2 was as follows.

CH ₄ 0.02 Nl / hr H ₂ 125.257 Nl / hr CO 37.749 Nl / hr CO ₂ 62.249 Nl / hr H ₂ O 274.746 Nl / hr Thus, the water vapor contained in the gas composition in the first stage discharge line 2 From the second stage onward, only methane gas was supplied to the inlet of each stage so as to maintain S / C = 2.0 with respect to the water vapor in the effluent gas from the upper stage.

In such an operating state of the fuel cell, gas components at the supply port and the discharge port of each stage from the second stage onward with each number were measured, and the results are shown in Table 1, respectively.

The total amount of hydrogen gas consumed in the power generation reaction in the internal reforming type multi-stage fuel cell power generator used in the present example was 229
It was 7.815 Nl / hr.

At this time, the supply amount of CH ₄ was 826.248 Nl / hr, and the supply amount of H ₂ O was
Since it is 200.000Nl / hr, H ₂ O / CH ₄ = 200.000 / 826.248 =
It was 0.242. However, in each stage, H ₂ O / CH ₄ = 2.0 is maintained as described above.

Comparative Example 1 As shown in FIG. 3, a reforming and power generation reaction were performed in a conventional molten carbonate type fuel cell power generation device composed of one stage of an internal reforming type.

The methane gas and water vapor introduced into the reforming reaction were methane gas and water vapor, respectively, as shown below so that the amount of hydrogen gas consumed in the power generation reaction was the same as in Example 1.

CH ₄ 969.587 Nl / hr H ₂ O 1939.174 Nl / hr A reforming reaction was performed with this gas composition, and power generation was performed using 75% of hydrogen gas as in Example 1. The gas composition at the outlet of the fuel cell after the completion of the electrode reaction was as follows.

CH ₄ 0.019Nl / hr H ₂ 1214.478Nl / hr CO 366.009Nl / hr CO ₂ 603.558Nl / hr H ₂ O 2663.844Nl / hr Power generation reaction of the internal reforming type single-stage fuel cell power generator used in this comparative example The total amount of hydrogen gas consumed in 2297.815Nl / h
r.

At this time, the supply amount of CH ₄ is 969.587 Nl / hr, and the supply amount of H ₂ O is
Since it is 1939.174 Nl / hr, H ₂ O / CH ₄ = 1939.174 / 969.587
= 2.0.

As described above, when the fuel cell is operated with the same hydrogen consumption and the same power generation amount in both the example and the comparative example, according to the present invention that uses the steam generated in the upper stage even if the power generation amount is the same, the steam usage amount is reduced. It can be seen that the savings are extremely high. As described above, the fuel cell power generation system according to the present invention utilizes steam generated by the power generation reaction, and secures a sufficient amount of steam necessary for reforming hydrocarbons.
Steam supplied from outside can be significantly reduced.

[Effects of the Invention] As described above, the fuel cell power generation system of the present invention has the following effects.

As the steam required for the reforming of hydrocarbons is generated at the fuel electrode of the fuel cell, the amount of steam used can be reduced.

Since the hydrogen partial pressure is averaged, a constant electromotive force is obtained.

The present invention can be suitably applied to not only a solid electrolyte fuel cell but also a molten carbonate fuel cell.

The same effect can be obtained not only with the internal reforming type fuel cell but also with the external reforming type in which a reforming device is provided between the fuel cells.

[Brief description of the drawings]

FIG. 1 is a schematic view of an internal reforming type molten carbonate fuel cell showing a power generation system according to the present invention, and FIG. 2 is a multistage internal reforming type molten carbonate used in Examples. FIG. 3 is a schematic view of a conventional internal reforming type molten carbonate fuel cell composed of one stage, and FIG. 4 is a conventional molten carbonate type fuel cell. It is sectional drawing which shows the structure of a battery. In the figure: 1, 2: fuel cell, 1a, 2a: fuel chamber, 1b, 2b: air chamber, 3: fuel gas supply line, 4: steam supply line, 5: compressor, 6: cooler, 7: Gas-liquid separator 8a, 8b: combustor, 9a, 9b: air supply line, 10a, 10b are exhaust gas lines.

Claims (2)

(57) [Claims] 1. A power generation system using a fuel cell,
The fuel cell is divided into two or more stages and installed, and hydrocarbons are added to a gas containing steam and carbon dioxide gas flowing out of the fuel chamber of the upstream fuel cell, and used as a raw material for the reforming reaction of the downstream fuel cell to generate power. A power generation system for a fuel cell. 2. The power generation system according to claim 1, wherein a gas containing water vapor and carbon dioxide flowing out of the fuel chamber is recycled and used as a raw material for a reforming reaction of each fuel cell.